linux-kernel - Re: [Patch] document ext3 requirements (was Re: [RFD] Incremental fsck)

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Message-ID: <20080117073838.GL3351@webber.adilger.int>
Date:	Thu, 17 Jan 2008 00:38:38 -0700
From:	Andreas Dilger <adilger@....com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Daniel Phillips <phillips@...gle.com>, Pavel Machek <pavel@....cz>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Theodore Tso <tytso@....edu>, Al Boldi <a1426z@...ab.com>,
	Valerie Henson <val.henson@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Patch] document ext3 requirements (was Re: [RFD] Incremental
	fsck)

On Jan 15, 2008  22:05 -0500, Rik van Riel wrote:
> With a filesystem that is compartmentalized and checksums metadata,
> I believe that an online fsck is absolutely worth having.
> 
> Instead of the filesystem resorting to mounting the whole volume
> read-only on certain errors, part of the filesystem can be offlined
> while an fsck runs.  This could even be done automatically in many
> situations.

In ext4 we store per-group state flags in each group, and the group
descriptor is checksummed (to detect spurious flags), so it should
be relatively straight forward to store an "error" flag in a single
group and have it become read-only.

As a starting point, it would be worthwhile to check instances of
ext4_error() to see how many of them can be targetted at a specific
group.  I'd guess most of them could be (corrupt inodes, directory
and indirect blocks, incorrect bitmaps).

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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